1. Field of the Invention
The present invention relates to an alignment mark used in an LSI manufacturing process, and an aligning method using the alignment mark.
2. Description of the Related Art
As show in FIGS. 7 and 8, a conventional alignment mark consists of a plurality of mark portions 1 on the surface of a substrate 2. The mark portions 1 are recessed portions having the same depth. A laser beam illuminates the substrate 2 perpendicular to the substrate 2, and is scanned along the surface of the substrate 2. When a laser beam illuminates an area 2 including the alignment mark, as shown in FIG. 8, light is diffracted due to the presence of the alignment mark, decreasing the intensity of light reflected by the surface of the substrate 2 perpendicular thereto. It is thus possible to detect the alignment mark by monitoring the intensity of light reflected by the substrate 2. Alignment of the substrate 2 is performed on this basis.
However, in the LSI manufacturing process, various films, such as a metal film 4 shown in FIG. 9, are formed on the surface of the substrate 2 for forming circuits. Since such a metal film 4 is also deposited within each of the mark portions 1 of the alignment mark, the apparent shape of the alignment mark is gradually deformed as the formation of the film on the surface of the substrate 2 proceeds. Particularly, when the metal is deposited obliquely with respect to the alignment mark, as shown in FIG. 9, the amount of metal deposited within each of the mark portions 1 is non-uniform. Consequently, a center O.sub.2 of the alignment mark which appears on the surface of the metal film 4 deviates from a true center O.sub.1 of the alignment mark on the surface of the substrate 2, and the alignment accuracy deteriorates.